1. Field of the Invention
The present invention generally relates to a method of guaranteeing security over a tree-structured point-to-multipoint network. More particularly, the present invention relates to a method of transmitting security data for authenticating and guaranteeing the confidentiality of data transmitted from a source point to a target point.
2. Description of the Related Art
A plurality of network devices connected to a single network device as a root is defined as a tree-structured network. One example of the tree-structured point-to-multipoint network is a passive optical network (PON), which includes one or more ONUs (Optical Network Units) connected to one OLT (Optical Line Terminal). FIG. 1 illustrates the configuration of a typical PON.
As illustrated in FIG. 1, the PON can comprise one OLT 100, ONUs 110-1 to 110-3 connected to the OLT 100, and end users 120-1 to 120-3 connected to the respective ONUs 110- 1 to 110-3. Although each ONU is shown to be connected to one end user in FIG. 1, a plurality of end users can be connected to one ONU and the ONUs 110-1 to 110-3 and the end users 120-1 to 120-3 can be connected in a point-to-multipoint tree structure.
In the existing Ethernet passive optical network (EPON) which transmits an 802.3 Ethernet frame over a tree-structured point-to-multipoint network, ONU data is accessed according to a TDM (Time Division Multiplexing) scheme for uplink transmission, and a “broadcast and selection” protocol for downlink transmission. In the downlink transmission, the OLT 100 broadcasts a downlink message destined for a particular ONU to all ONUs 110-1 to 110-3 and the intended ONU receives the message by a filtering process. However, in this arrangement, other ONUs may receive the same data. Therefore, privacy is not guaranteed.
In the uplink transmission, only an unauthenticated ONU can be connected. However, any one of the ONUs 110-1 to 110-3, disguising itself as a different ONU by spoofing its identity, can launch “denial of service” attacks or access material or resources, thus undermining the security. To prevent these problems, different keys to the ONUs 110-1 to 110-3 are distributed through an authentication procedure so that encrypted messages using the keys can be authenticated for downlink signals and uplink messages.
Encryption technologies for ATM (Asynchronous Transfer Mode) PON have been already standardized and specified in ITU-T G.983.1. However, encryption and its implementation for the EPON which transmits an Ethernet frame over a physical plant known as PON are still undefined.
FIG. 2 illustrates an exemplary message structure of a typical Ethernet frame format.
Methods of encrypting an FCS (Frame Check Sequence) as well as a message have been proposed in encrypting the message using an encryption algorithm. If an unauthenticated attacker (e.g., an unauthenticated ONU) is connected to the OLT 100 and transmits messages using an unauthenticated key, the OLT 100 decodes them using an authenticated key and then compares the check sum of the message with an FCS value. If they are different, an FCS check error is generated notifying the OLT 100 that the data or the data source is not authenticated. With the additional encryption of the FCS, however, the same FCS check error can be generated in other cases, such as a link failure and device defects. In these cases, the cause of FCS error cannot be identified. As a result, uncertainty in the cause of error leads to a link management problem.